(AH_2N-H-NH_2B)^+A,B=H,F,CH_3的質子轉移理論研究

Theoretical Study of Proton Transfer in (NH_2 AHNH_2B)+ Complex Ions

郭進祥(Jin-Xiang Kuo) ； 何嘉仁(Jia-Jen He)

《化學》 56卷3期 (1998/09) Pp. 157-166

https://doi.org/10.6623/chem.1998022

摘要

本研究藉由ab initio理論計算的方法，探討質子在兩個NH_2A、NH_2B (A, B = H, F, CH_3)分子問轉移的性質。在MP2/6 - 31G(d)層級得到A = H, B = F及A = H, B = CH_3的質子化雙聚體系統中，質子是靠在質子化能較大的一邊，質子轉移曲總因兩邊質子化能相差較大是單位能井。A與B相同分別為H，F,CH_3質子轉移曲線則是雙位能井。未取代時(A，B = H)質子恰在兩個氮原子的連線上，即δ(N^R N^L H^m ) = 0°，氟原子取代時δ = 19.3°，甲基取代時δ = 0.5°。質子轉移時兩個氮原子間的距離分別由2.731、2.708及2.735 Å縮小至2.614、2.593及2.614 Å。其質子轉移的能障分別是1.1 0、2.30及1.13 kcal/mol。拉電子基( F ) 及推電子基(CH_3)都使能障升高，F的取代使能障升高較多。

並列摘要

Ab initio theoretical method was performed to calculate the proton transfer property of (NH_2 AHNH_2B)^+ complex ion (wher A, B=H, F, and CH_3) . In the complex ions where A=H, B=F and A=H. B=CH_3, the proton resides on the site of the NH_2X unit (X=A or B) having greater proton energy. The potential profile thus becomes a single well. However, if A=B, either H, F, or CH_3, there exists two minima and a double well potential is formed in the process of proton transfer of the complexes. In (NH_3 HNH_3)^+ the proton resides on the line connecting the two N atoms, that is δ(N^R N^L H^M)=0° , whereas in (NH_2FHNH_2F)^+, δ=19.3°, andδ=0.5°, in (NH2CH3HNH2CH3)+ ion. The distance of the two N atoms shrinks diring the process of proton transfer, such as from 2.731, 2.708, and 2.735 Å for A, B=H, F, and CH_3, respectively, to 2.614, 2.593, and 2.614 Å . The barriers for proton transfer are 1.10, 2.30, and 1.13 kcal /mol for A, B=H, F, and CH_3, respectively. Proton transfer proceeds with greater difficulty in fluoro-substituted complex than in the non-substituted and methyl-substituted complexes.